GM workers went on strike June 5, claiming health and safety violations at two parts plants in Flint, Mich.

Parts shortages from the two plants have now idled 192,300 workers and shut down almost all GM's auto and truck production in North America.

At the last US GM plant in operation, Saturn in Spring Hill, Tenn., union leaders were deciding, at press time, whether to join the strike.

Supplies of cars, and especially trucks, at many GM dealers are running so short that this month marks a critical turning point, says Mr. Anwyl.

If strikes go on much longer "we could see short-term increases" in both new- and used-car prices, he says.

Overall, car prices have been softening this year because there are so many cars rolling off the assembly line - a 30 to 40 percent overcapacity in production. "Curiously, that's about GM's market share, though I'm not saying they're related," Anwyl says.